Wallowing is the immersion of the body in small water holes or mud (termed wallows) and it is a widespread behaviour among large Mammalian herbivores, and also fulfils a variety of functions for the Javan Rhinos. The main known reasons for wallowing include protection against the sun, hermoregulation, removal of ectoparasites, skin conditioning, and olfactory advertisement by impregnating the skin with the urine-rich mud or water of the wallow. Direct observation of Javan Rhinos is extremely difficult due to their rarity, currently there are only 72 Animals, and remote rainforest habitat. Therefore, camera trap videos are the main remote sensing tool for studying Javan Rhinos in the wild. The Javan Rhino is an active wallower and based on camera trap evidence in Ujung Kulon National Park, West Java, may share and use the same or multiple wallows, which increases the potential of interaction, or at least be able to find olfactory messages left by other Rhinos at those sites.
Research on Javan Rhino behaviour at wallows has been limited to date, due to their rarity, shy nature and highly protected status. The little available Javan Rhino wallowing information has been included as a component of broader ecological and habitat studies. A study published in 2010 undertook preliminary behaviour observations of Javan Rhino based on camera trap video surveys, including surveillance at some wallows in the peninsula area of Ujung Kulon National Park. The wallowing behaviour of the congeneric Greater One-horned Rhino, Rhinoceros unicornis, has been well researched, as have the two African species and Sumatran Rhino, Dicerorhinus sumatrensis. All five Rhino species vocalise in various categories including puffing, snorting, growling and harmonic calls. Based on limited research Javan Rhinos are considered the least vocal Rhino species. This suggests the idea that the Javan Rhinos have a very limited repertoire of calls could be due to its geographical remoteness, small numbers and very limited research on the species. Field studies of the Greater One-horned Rhino have identified a range of 10 calls including snorts, honks, bleats, squeak-pant and a moo-grunt commonly used by mothers and calves. Currently, our knowledge of Javan Rhino social structure, behaviour and communication has been restricted to a few historic accounts mostly from the 1900’s. For example, in 1969 Rudolf Schenkel and Lotte Schenkel-Hulliger, suggested Javan Rhino were mostly solitary, independent, or, were 'loosely associated nomads'. Initial work by Hartmann Ammann in the 1980s described five distinct Javan Rhino calls, including ‘neigh,’ the ‘loud blowing whistle’ of Schenkel and Schenkel-Hulliger; ‘bleat,’ a contact call between mother and young; ‘snort,’ made separately or in a series; ‘shriek,’ a possible response to a threat; and ‘lip vibration’, similar in sound to that made by Horses.
Located in Western Java, Indonesia, Ujung Kulon National Park, with a total area of over 120 000 ha (1200 km²), encompasses 76 214 ha (762.14 km²) of terrestrial areas and 44 337 ha (443.37 km²) of marine habitat. An area of 30 000 ha (300 km²) in the Ujung Kulon peninsula provides the core rainforest habitat for the last remaining Javan Rhinos globally. The climate of Ujung Kulon is tropical with a seasonal mean annual rainfall of 3250 mm, mean temperature range of 25–30°C and relative humidity of 65–100%. In 2010, a 5100 ha (51 km²) Javan Rhino Research and Study Conservation Area was established within the greater Gunung Honje area of Ujung Kulon National Park. This included installation of an 8 km long Rhino proof fence to exclude domestic stock, protect the Javan Rhino Research and Study Conservation Area and enclose the Rhinos safely in the Park, area. The Javan Rhino Research and Study Conservation Area site was established as a staging area for translocation of a subset of the Rhino population to an appropriate site, preferably within its historic range.
In a paper published in the journal Pachyderm on 8 October 2020, Steven Wilson of the Biodiversity Research Group at the University of Queensland, and the Land, Biodiversity and Indigenous and River Health Programs at the Goulburn Broken Catchment Management Authority, Georgina Hockings, also of the Biodiversity Research Group at the University of Queensland, Jo-Anne Deretic, also of the Land, Biodiversity and Indigenous and River Health Programs at the Goulburn Broken Catchment Management Authority, and Salit Kark, again of the Biodiversity Research Group at the University of Queensland, present the results of a study of the behaviour of Rhinos at wallows in the Javan Rhino Research and Study Conservation Area.
Wilson et al. actively explored the Javan Rhino Research and Study Conservation Area area on foot and determined the locations of 35 wallows between 2015–2017. Each wallow was spatially mapped, and its characteristics were recorded using a Garmin GPS Maps 62 sc GPS unit and maps were created using ArcMap 10.5 software. Wilson et al. recorded Rhino wallow visitation frequency and behaviour characteristics including vocalisation using camera trap video. Wallowing behaviour was also recorded using camera trap video at active wallows in the Ujung Kulon peninsula area of the Park (main Rhino population). Photographs were taken by using a Canon 50D digital camera of each of the 35 wallows to quantify the wallow features. Wilson et al. recorded the location and physical features of wallows, including topography, vegetation, soil type, shade/canopy cover, elevation and ‘concealability’. Wilson et al. determined eight active wallow sites comprising 68 videos, and 23 forest locations with rhino activity captured via 69 videos.
Wilson et al.'s analysis of wallowing behaviour supports other studies on wallow behaviour in Rhinos, illustrating that wallows provide more than just a mud bath for the Javan Rhino, probably contributing to their very existence. Furthermore, in this study several behaviours, other than wallowing, were recorded at and around wallow sites, showing that wallows are also an important site for communication, On multiple occasions calling was recorded at one of the wallow sites, a total of 157 calls in the study period. Wilson et al. identified eight behavioural patterns (described as feeding, locomotion, comfort, vigilance, investigating environment, calling (vocalisation), smelling/sniffing, and breeding/courtship), and 11 sub-behavioural pattern categories at and near wallows from the 68 videos taken during the 2011–2015 period in the peninsula area of Ujung Kulon. The relationship between temporal observations, seasonal (wet/dry) observations were significant. Vegetation type observations were not significant.
The wallowing pattern of one male Rhino in particular known as ‘Samson’ was observed in the eastern Gunung Honje area of the national park via 255 videos taken during the period 12 November to 16 December 2016. Over this 30-day period Wilson et al. recorded 14 calls and observed bouts of wallowing behaviour ranging between 15 minutes and 6 hours, 9 minutes. ‘Samson’ visited the same wallow eight times during this period. Wallowing duration averaged 2.71 hours. There were no significant temporal differences in the wallow visits.
Based on and adapting Hartmann Ammann’s descriptions of wallows recorded in the Ujung Kulon peninsula, and our dataset of 35 wallows, Wilson et al. identified two wallow types. Mud wallow are clay based and contained mud with a thick viscous consistency to a depth averaging 14 cm. Rhino using and leaving the wallows were clearly coated with a film of mud. In mud wallows Animals were observed on camera video to periodically shake their heads and necks, presumably enabling mud to penetrate the deep skins folds. Water wallow are haracterised as holding water to depth averaging 18 cm. Water wallows often had a soft base of mud, which would be stirred up and mixed with active use. Rhino using and leaving the wallow were clearly coated with a film of water and the skin was clearly darkened by immersion in water.
Wilson et al. observed that wallows were often created at elevation and due to the undulating terrain in sloping areas with at least 75% shade cover. Often the rear of the wallow was dug out from a bank or edge, which enabled the wallow to be enlarged and expanded as necessary, horn marks in banks were often observed. Mud and water depth varied according to prevailing climatic conditions. The soil being latosolic (highly leached due to heavy rainfall), and clay-based meant run off during rain helped maintain a level of water and mud in the wallow. Shade at the wallow site was important as it influenced the temperature of water and mud; the percentage cover averaged 75%. The dominant over storey shade plant being Arenga Palm, Arenga obtusifolia. Wallow size depended on either single or multiple users, the latter often being many years old due to persistent use. The largest wallow recorded was eight metres long and seven metres wide. Average length of the wallows was 3.69 m, average width was 3.17 m.
When examining and comparing camera video recorded rhino calls, the number and frequency of recorded individual calls used by Rhino each year showed no statistical differences between observed and expected results. The authorities undertook no camera trap video recordings in 2012 due to limited field resources at the time. A greater diversity of call types occurred at wallowing sites compared to recordings made in the forest.
Examination of camera video trap recordings highlighted what appeared to be increased Rhino calling, especially during Rhino interactions at wallows. Wilson et al. identified seven call types from the audio video data recorded at wallows and categorised these where possible in a manner consistent with terms used by previous researchers. From these call recordings they were able to create sonograms, a first for the species.
Bleats are low intensity repeated contact call made by calves to females. Frequency band-width range is 100 Hz-4.5 kHz, (34 vocalisations).
The sniff-huff comprises a short nasal inhalation, followed by an exhaled huff. Used by both sexes when alone and in company. Often used when investigating the environment e.g. sniffing vegetation, or possible scent trails left by conspecifics. Frequency band width range is shorter than the snort or sigh, and ranges between 100 Hz-14.5 kHz, with most calls lasting under half a second (e.g. 0.2–0.5 seconds), (48 vocalisations).
The short pant is a short, often repeated air sounding call. Starting with a soft whistle sound at start of call. Recorded only in males to date. The frequency band width range varies between 100 Hz-12 kHz, with most repeated calls lasting under half a second (e.g. 0.1–0.3 seconds), (65 vocalisations).
The long hiss is an extended single, strong, air sounding, ear-piercing call. May infer a warning. Only recorded in adult females near approaching males to date. The frequency range varies between 100 Hz-11.5 kHz, with the single call lasting under one second (e.g. 0.7–0.8 seconds), (6 vocalisations).
The lip vibration is softer than a snort, may be a contact response, or indicates comfort e.g. when feeding. Lip vibrations appear to be mostly single calls. The frequency range varies between 100 Hz-5 kHz, with calls lasting under one second (e.g. 0.7–0.8 seconds), (5 vocalisations).
The sigh is an exhalation call, longer in duration to lip vibration, slow and softer in emphasis, comfortlike and may be used as an acknowledgement of call e.g. a response from a female to her calf. The frequency range varies between 100 Hz-12 kHz, with most calls lasting under one second (e.g. 0.2–1.056 seconds), (32 vocalisations).
The snort is a strong exhaled loud call may infer vocal dominance from adult male or female. The frequency bandwidth range varies between 100 Hz-12 kHz, with a single vocal lasting more than one second (e.g. 1.148 sec), (2 vocalisations).
Understanding behaviour is key in threatened species management and relocation. Identifying important requirements, such as wallowing and behaviours around them can be crucial in the success of future plans and conservation programs. This study shows that the activity of wallowing for Javan rhinos is an important component of their interactions, communication and fulfilment, which takes place throughout every month of the year. All five-Rhino species will utilise water bodies, muddy depressions, rivers and sandy areas for wallowing activity. During extended dry periods Javan Rhino will utilise riverine habitats and tidal waterways to manage heat stress, when mud and water wallows are not viable. The lower use of wallows in the morning period (6.00–12.00 am) identified by the significant statistical results for temporal (time of day) and seasonal (wet/dry) differences were not expected. Early morning, afternoon and evening periods were relatively even in their use patterns, and notably increased during the wet season (November–May) when compared to the dry season (June–October). While yet to be confirmed, it appears based on calf sightings Javan Rhino breed throughout the year so the use of wallows as scent-posts to communicate oestrus may be occurring. The two other Asian Rhino species, the Greater One-horned and Sumatran Rhino like Javan Rhino are solitary but would readily share a wallow with another Rhino without incident.
On several occasions Wilson et al. observed adult males approaching females using wallows, where they would vocalise a repeated ‘short pant’ call as they approached, and when close enough would use flehmen to determine the reproductive status of the female. Females with calves would respond to males with an agonistically vocalised ‘long hiss’. Males would then subdue their attention and share the wallow in harmony. Single females would regularly drink wallow water, often followed by flehmen, and on two occasions were observed eating mud (geophagy). Presumably, the drinking, geophagy and flehmen response is to determine the presence, and possibly dominance status of male rhinos. Based on their observations, Wilson et al. suggest that wallows are not created randomly by Rhino in the landscape. They recorded and observed some common wallow characteristics. For example, wallows are usually created at 30 m or greater elevation, in slightly sloping areas to allow water run-off. Rhinos create the wallow shape through digging and shaping the rear of the wallow from a bank or edge, which enabled the wallow to be enlarged and expanded as necessary, horn marks in the banks were often observed.
Shade at the wallow site was important as it influenced the temperature of water and mud. These factors contribute to thermoregulation benefits, the persistence of mud and water allowing urine and other scents to remain in situ for longer periods as well as the long-term maintenance of the wallow itself, extended its use and value as a key habitat feature.
As well as wallowing Javan Rhino would make behavioural adjustments to avoid heat stress. These would include, nocturnal foraging, resting in shade, and resting near coastal areas with cooling sea breezes. As a mostly solitary species, Javan Rhino communicates its presence via spray urination, dung deposition and pedal scent gland secretions. However, it remains unclear whether only dominant adult males spray urine. Wilson et al. detected adult males approaching a wallow and spraying urine on vegetation at least three metres behind itself. As an often-shared habitat resource, calling from (and close by) wallows has been shown to escalate due to increased opportunity to meet other Rhino either wanting to thermoregulate. or interact in some way. The 157 individual call recordings, while low in number, have provided important new insights into the call repertoire of Javan Rhino. Camera video trapping cannot replace direct observation, however it can provide valuable insight into Javan Rhino communication behaviour in a rainforest environment and a shy species, such as the Javan Rhino that is rarely observed in nature. A recent study by Ivana Cinková and Richard Policht suggested that the pant calls of Southern White Rhino, provides conspecific information about the caller’s sex, age class and social context. Wilson et al.'s data suggests that the ‘short pant’ calls of Javan Rhino may convey similar information, however more research is needed to analyse this specific call.
The recorded calls highlight the importance of filling the gap of knowledge regarding Javan Rhino communication, and present a base to build further understanding of Javan Rhino ecology and social dynamics. Because there are very few direct observations of Javan Rhinos this makes comparisons difficult. The implications of this wallow data are obvious. The baseline dataset of 35 wallows and their characteristics are valuable. Translocation of Javan Rhino into new or former historic ranges needs to include the important criterion in site selection, that sites are selected that enable the long-term maintenance of wallows is critical. This wallow data is important for future conservation efforts, and crucially, the development and identification of suitable Rhino habitat areas and future translocation plans of Animals to new sites.
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